Digital video/audio recording and reproducing apparatus

ABSTRACT

A digital video/audio recording and reproducing apparatus comprising a video signal high-efficiency encoder having a variable reduction rate, an audio signal high-efficiency encoder having a variable reduction rate, and a controller for controlling the reduction rates in both of the high-efficiency encoders. The reduction rates in both of the high-efficiency encoders are controlled in such a manner that the sum of the information amount of the video signal and that of the audio signal, after high-efficiency encoding, is maintained constant. When recording multi-channel audio signals, the reduction rates in both of the high-efficiency encoders are controlled according to the number of audio signal channels to be recorded. The high frequency components of the high-efficiency encoded video and audio signals are recorded at the end portions of recording tracks on a magnetic tape, while the low frequency components thereof are recorded in the central portion of the recording tracks.

This application is a divisional of copending application Ser. No.08/190,545, filed on Feb. 2, 1994, now U.S. Pat. No. 5,434,716, whichwas a Rule 60 continuation of Ser. No. 07/894,575, now U.S. Pat. No.5,309,290, filed Jun. 5, 1992, the entire contents of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital video/audio recording andreproducing apparatus for compressing and encoding digitized video andaudio signals, recording the thus encoded data on a recording mediumsuch as a magnetic tape, and reproducing the data recorded on therecording medium.

2. Description of Related Art

It is known to provide a digital video/audio recording and reproducingapparatus for digitizing video and audio signals simultaneously,recording the digitized signals on a recording medium such as a magnetictape, magnetic disk, or optical disk, and reproducing simultaneouslyboth the video and audio signals recorded on the recording medium forconversion into an analog representation. FIG. 1 is a block diagramshowing the configuration of such a known digital video/audio recordingand reproducing apparatus, disclosed in the July 1988 issue of HoshoGijutsu (Broadcast Technology).

In FIG. 1, the numerals 1 and 2 designate a video A/D converter and anaudio A/D converter, respectively, for converting an input analog videosignal and an input four-channel analog audio signal into a digitalrepresentation. The video signal digitized by the video A/D converter 1is supplied to a C2 encoder 3, which derives a C2 parity in theerror-correction encoding of the video signal, appends it to the videosignal, and delivers the video signal with the C2 parity to aninterleave 4 where the video signal is shuffled. The audio signaldigitized by the audio A/D converter 2 is supplied to an audioerror-correction encoder 5 where the digitized audio signal iserror-correction encoded. The video signal shuffled in the interleave 4and the audio signal error-correction encoded by the audioerror-correction encoder 5 are combined in an adder and delivered to aC1 encoder 6. The C1 encoder 6 derives a C1 parity for the combineddata, appends it to the data, and delivers the data with the C1 parityto a modulator 7 where the error-correction encoded data is encoded forrecording. The data encoded for recording is recorded on a magnetic tape8 by means of a magnetic head 10 mounted on a rotating drum 9.

The reference numerals 11 to 19 indicate components comprising areproduction system, wherein the numeral 11 designates a demodulator fordecoding the replay data played back from the magnetic tape 8. The datathus decoded is directed to a C1 decoder 12 which performserror-correction based on the C1 parity word and delivers theerror-corrected replay data to an A/V separation circuit 13. The A/Vseparation circuit 13 separates the replay data into a video signal andan audio signal and supplies the video signal to a deinterleave 14 andthe audio signal to an audio error-correction decoder 18. Thedeinterleave 14 deshuffles the supplied video signal and delivers thedeshuffled video signal to a C2 decoder 15 which performserror-correction based on the C2 parity word and delivers the errorcorrected video signal to an interpolation circuit 16. The interpolationcircuit 16 performs interpolation on the video signal if there are anyuncorrectable errors, and after processing, delivers the video signal toa video D/A converter 17 which converts the digital video signal into ananalog signal for output. The audio error-correction decoder 18 performserror-correction on the supplied audio signal and delivers theerror-corrected audio signal to an audio D/A converter 19 which convertsthe digital audio signal into an analog signal for output.

The operation of the above apparatus will now be described.

The input analog video signal is converted into a digital signal by thevideo A/D converter 1, and the digitized video signal is supplied to theC2 encoder 3 which appends the C2 parity for error correction. The videosignal with the C2 parity is read into the interleave 4 where prescribedshuffling is performed on the video signal, after which the video signalis fed to the adder. On the other hand, the input analog audio signal isdigitized by the A/D converter 2 and error-correction encoded by theaudio error-correction encoder 5, after which the audio signal is fed tothe adder where it is combined with the video signal. The combined datais fed to the C1 encoder 6 where the C1 parity is appended. The shuffledand error-correction encoded data is supplied to the modulator 7 whichencodes it for recording. The data is now recorded on the magnetic tape8 by means of the magnetic head 10. FIG. 2 shows the signal recordingformat recorded on the magnetic tape 8. The video signal and thefour-channel audio signal are recorded in different areas on the sametrack, the audio signal being recorded outwardly of the ends of thevideo signal.

In the reproduction system, the digital data played back by the magnetichead 10 is fed to the demodulator 11 for decoding, after which the C1decoder 12 performs error correction based on the C1 parity word. Theoutput data from the C1 decoder 12 is separated into a video signal andan audio signal by the A/V separation circuit 13. The audio signal isprocessed by the audio error-correction decoder 18 and then converted bythe audio D/A converter into a four-channlel analog signal for soundreproduction. On the other hand, the video signal is deshuffled by thedeinterleave 14 to rearrange it into the original order, after which theC2 decoder 15 performs error correction based on the C2 parity word; ifthere are any uncorrectable errors, error flags are attached, and theinterpolation circuit 16 performs one-dimensional or two-dimensionalinterpolation on the video signal, the thus processed video signal thenbeing converted by the video D/A converter 17 into an analog videosignal for picture reproduction.

However, the conventional digital video/audio recording and reproducingapparatus having the above construction has the disadvantage that inorder to reduce the overall size of the apparatus, if the size of therecording medium (magnetic tape) is made smaller, a shorter recordingtime will have to be tolerated, and if the size of the magnetic head isreduced, the recording data transfer rate (information amount) willdrop, resulting in degradation in both the picture and the soundquality.

Furthermore, because of the fixed structure of the video signalrecording areas and the audio signal recording areas on the recordingmedium (magnetic tape), as shown in FIG. 2, the maximum number ofrecordable audio signal channels is determined by the recording format,which gives rise to the problem that the number of audio signal channelscannot be increased beyond the predetermined maximum number; therefore,a digital video/audio recording and reproducing apparatus designed fortwo-channel audio recording, for example, cannot be used for recordingthree or more audio signal channels by using the same recording format.

Generally, in magnetic tape recording using a rotating magnetic head,the reproduction signal quality obtained from the ends of the recordingtracks is inferior to that obtained from the center thereof, sinceerrors frequently occur in the reproduction signal from the ends of thetracks. Presumably, this is because the magnetic head to magnetic tapecontact characteristic is unstable at the ends of the recording trackscompared to the center thereof. In digital recording and reproducingapparatus for business use, since the recording density is set at arelatively low rate to maintain reliability, the signal qualityacceptable for practical use can be obtained even from the ends of therecording tracks. However, the recording format having audio signalsrecorded at the ends of the tracks as shown in FIG. 2, when applied to adigital video/audio recording and reproducing apparatus designed for ahigher recording density, gives rise to the problem that there occursdegradation in the sound quality since the signal quality degrades atthe ends of the tracks. On the other hand, in a recording format inwhich the video signal recording areas are disposed at the ends of therecording tracks, degradation in the picture quality will result. Thus,the degradation of the reproduction signal quality at the ends of thetracks has the problem of causing errors in the reproduced video oraudio signals.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a digitalvideo/audio recording and reproducing apparatus having a predeterminedtransfer rate for signal recording and reproduction, that is, in thecase of magnetic tape, for example, a predetermined tape speed and apredetermined recording density, and capable of simultaneously recordingvideo and audio signals.

It is another object of the invention to provide a digital video/audiorecording and reproducing apparatus having a predetermined transfer ratefor signal recording and reproduction and capable of simultaneouslyrecording video signals and multi-channel audio signals such as twochannels, four channels, etc.

It is a further object of the invention to provide a digital video/audiorecording and reproducing apparatus wherein errors occurring at the endsof the recording tracks do not lead to particularly noticeable errors inthe reproduced video and audio signals, that is, as visible or audiblenoise in picture or sound reproduction.

In accordance with one preferred mode of the invention, there isprovided a digital video/audio recording and reproducing apparatus whichcomprises a video signal high-efficiency encoding means having avariable reduction rate, an audio signal high-efficiency encoding meanshaving a variable reduction rate, and a means for controlling thereduction rates in both of the high-efficiency encoding means accordingto the information amounts of the video and audio signals. The reductionrates in both of the high-efficiency encoding means are controlled insuch a manner that the sum of the information amount of the encodedvideo signal and that of the encoded audio signal is maintainedconstant. When the information amount of the encoded video signal issmaller than that achieved by a predetermined reduction rate, the audiosignal is also recorded, with a decreased reduction rate, in a recordingarea originally provided for recording of the video signal. On the otherhand, when the information amount of the encoded audio signal is smallerthan that achieved by a predetermined reduction rate, the video signalis also recorded, with a decreased reduction rate, in a recording areaoriginally provided for recording of the audio signal. Thus, therecording medium having a limited information storing capacity iseffectively utilized without leaving any recording areas unrecorded, sothat the degradation of the video and audio signal quality is held to aminimum.

In another preferred mode of the invention, there is provided a digitalvideo/audio recording and reproducing apparatus which comprises a videosignal high-efficiency encoding means having a variable reduction rate,a means for selecting audio signal channels to be recorded from among aplurality of audio signal channels, and a means for controlling thereduction rate in the high-efficiency encoding means according to thenumber of selected audio signal channels. The reduction rate in thehigh-efficiency encoding means is controlled in such a manner that thesum of the information amount of the encoded video signal and that ofthe encoded audio signal is maintained constant. When the number ofaudio signal channels to be recorded increases, that is, when the amountof audio information to be recorded increases, the reduction rate in thevideo signal high-efficiency encoding means is raised; conversely, whenthe number of audio signal channels to be recorded decreases, that is,when the amount of audio information to be recorded decreases, thereduction rate in the high-efficiency encoding means is lowered. Despitethe change of the number of audio signal channels to be recorded, thesum of the information amount of the encoded video signal and that ofthe encoded audio signal is maintained constant, so that the videosignal is recorded simultaneously with the audio signal having thedesired number of channels, with a minimum degradation in the picturequality. The apparatus may further include a high-efficiency encodingmeans for encoding the audio signal of selected channels, in which casethe reduction rate in this high-efficiency encoding means is alsocontrolled according to the number of selected audio signal channels.

In a further preferred mode of the invention, there is provided adigital video/audio recording and reproducing apparatus which comprisesa vide o signal high-efficiency encoding means for performing atransform to the frequency axis for encoding, an audio signalhigh-efficiency encoding means for performing a transform to thefrequency axis for encoding, and a sorting means for reordering thecomponents of the encoded video and audio signals. The encoded videosignal is recorded in sequence from high to low frequency componentsstarting at one end of a recording track on magnetic tape whereas theencoded audio signal is recorded in sequence from high to low frequencycomponents starting at the other end of the recording track. This onlycauses errors in reproduction in the high frequency domains of the videoand audio signals, and no appreciable errors appear in the reproducedpicture or sound as a whole.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a conventionaldigital video/audio recording and reproducing apparatus.

FIG. 2 is a diagram showing a recording format on a magnetic tapeaccording to the conventional digital video/audio recording andreproducing apparatus.

FIG. 3 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a firstembodiment of the invention.

FIG. 4 is a schematic diagram showing the internal configuration of ahigh-efficiency encoder shown in FIG. 3.

FIG. 5 is a schematic diagram showing the internal configuration of acontroller shown in FIG. 3.

FIGS. 6(a)-6(c) are conceptual diagrams showing the amounts ofinformation when high-efficiency encoding and data compression areperformed on video and audio signals.

FIG. 7 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a secondembodiment of the invention.

FIG. 8 is a schematic diagram showing the internal configuration of ahigh-efficiency encoder shown in FIG. 7.

FIG. 9 is a conceptual diagram showing the amount of information whenhigh-efficiency encoding and data compression are performed on a videosignal according to the second embodiment.

FIGS. 10(a)-10(b) are a recording format on a magnetic tape according tothe second embodiment.

FIG. 11 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a thirdembodiment of the invention.

FIG. 12 is a schematic diagram showing the internal configuration of acontroller shown in FIG. 11.

FIG. 13 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a fourthembodiment of the invention.

FIG. 14 is a diagram showing the arrangement pattern of a video signaland an audio signal recorded on a recording track according to thefourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings.

Embodiment 1

FIG. 3 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a firstembodiment of the invention. The same reference numerals as used in FIG.1 designate corresponding components. In FIG. 3, the reference numerals1 and 2 designate a video A/D converter and an audio A/D converter,respectively, for converting an input analog video signal and an inputanalog audio signal into a digital representation. The video signaldigitized by the video A/D converter 1 is delivered to a videointerleave 21 which divides the video signal into blocks eachrepresenting a plurality of pixels and which performs shuffling on eachof the blocks. The video signal read from the video interleave 21 isdirected to a video high-efficiency encoder 22 where data compression isperformed on each block, the compressed video signal then beingdelivered to an adder 32. On the other hand, the audio signal digitizedby the audio A/D converter 2 is delivered to an audio interleave 23which divides the audio signal into blocks each representing a pluralityof pixels and which performs shuffling on each of the blocks. The audiosignal read from the audio interleave 23 is directed to an audiohigh-efficiency encoder 24 where data compression is performed on eachblock, the compressed audio signal then being delivered to the adder 32.The adder 32 combines the encoded video signal with the encoded audiosignal and supplies the combined data to an error-correction encoder 25.The error-correction encoder 25 performs error-correction encoding onthe data and delivers the encoded data to a modulator 7 where theerror-correction encoded data is encoded for recording. The data thusencoded for recording is recorded on a magnetic tape 8 by means of amagnetic head 10 mounted on a rotating drum 9.

In the reproduction system, the numeral 11 designates a demodulator fordecoding the replay data played back from the magnetic tape 8, the datathus decoded being delivered to an error-correction decoder 26. Theerror-correction decoder 26 corrects errors in the video and audiosignals and supplies the corrected video and audio signals to an A/Vseparation circuit 13. The A/V separation circuit 13 separates thesupplied data into the video signal and the audio signal and directs thevideo signal to a video high-efficiency decoder 27 and the audio signalto an audio high-efficiency decoder 29. The video high-efficiencydecoder 27 performs data expansion on the compressed video signal anddelivers the expanded video signal to a video deinterleave 28 wheredeshuffling is performed on each of the video blocks. The video signalfrom the video deinterleave 28 is read into an interpolation circuit 16which performs interpolation on the video signal in the presence ofuncorrectable errors and delivers the processed video signal to a videoD/A converter 17. The video D/A converter 17 converts the digital videosignal into an analog representation for output. The audiohigh-efficiency decoder 29 performs data expansion on the compressedaudio signal and delivers the expanded audio signal to an audiodeinterleave 30. The audio deinterleave 30 performs deshuffling on eachof the audio blocks and delivers the deshuffled audio signal to an audioD/A converter 19 which converts the digital audio signal into an analogrepresentation for output.

The numeral 31 designates a controller for controlling the reductionrate in the video and audio high-efficiency encoders 22 and 24. Anestimated amount of information is input to the controller 31 from eachof the video and audio high-efficiency encoders 22 and 24, and based onthis input value, the controller 31 supplies control values to the videoand audio high-efficiency encoders 22, 24 and decoders 27, 29.

FIG. 4 is a schematic diagram showing the internal configuration of thevideo high-efficiency encoder 22 (or the audio high-efficiency encoder24) in the recording system shown in FIG. 3. As shown, the videohigh-efficiency encoder 22 (or the audio high-efficiency encoder 24)comprises: an orthogonal transform circuit 41 for performing anorthogonal transform, such as a discrete cosine transform (DCT), on eachblock of the video signal (or the audio signal); an information amountestimation circuit 43 for estimating the information amount of the videosignal (or the audio signal) on the basis of transform coefficientssupplied from the orthogonal transform circuit 41; a variable-lengthencoding circuit 42 for encoding the transform coefficients from theorthogonal transform circuit 41 to adaptively quantizing them inaccordance with the estimated amount of information supplied from theinformation amount estimation circuit 43; and a subtractor 44 forobtaining a free amount of information by calculating the differencebetween the estimated information amount of the video signal (or theaudio signal), given from the information amount estimation circuit 43,and the reference amount of information given from the controller 31 asa set value for the video signal (or the audio signal) informationamount.

FIG. 5 is a schematic diagram showing the internal configuration of thecontroller 31. As shown, the controller 31 comprises: a referenceinformation amount setting circuit 45 for setting the reference amountsof information for the video and audio signals; a subtractor 46 forcalculating the difference between a value fed back from the audiohigh-efficiency encoder 24, representing the free amount of informationin audio recording, and the reference amount of information for thevideo signal, given from the reference information amount settingcircuit 45, and for feeding the difference to the video high-efficiencyencoder 22; and a subtractor 47 for calculating the difference between avalue fed back from the video high-efficiency encoder 22, representingthe free amount of information in video recording, and the referenceamount of information for the audio signal, given from the referenceinformation amount setting circuit 45, and for feeding the difference tothe audio high-efficiency encoder 24.

The operation of the apparatus will now be described below.

In the recording system, the video signal (about 100 Mbps) digitized, asin the prior art example, by the video A/D converter 1 is delivered tothe video interleave 21 which divides the video signal into blocks eachrepresenting a plurality of pixels and which performs shuffling on eachof the blocks. The thus divided video signal is then compressed andencoded by the video high-efficiency encoder 22. In the videohigh-efficiency encoder 22, an orthogonal transform is performed by theorthogonal transform circuit 41; in this case, the video signal isdivided into blocks of 8 pixels×8 lines, which allows for a highreduction rate and is reasonable in terms of hardware. The shuffling bythe video interleave 21 is performed in order to randomize the videosignal and thereby achieve a higher degree of accuracy in the estimationof the information amount by the information amount estimation circuit43. Since the information amount is uniformly distributed as a result ofthe shuffling, it is easy to estimate the entire amount of informationfrom only a part of the information. After the orthogonal transformationby the orthogonal transform circuit 41, the variable-length encodingcircuit 42, which controls the word length, i.e. the number of bits forquantizing the transform coefficients, etc., compresses the video signalin accordance with the estimated amount of information from theinformation amount estimation circuit 43 so that the data size iscompressed to the reference amount of information set by the controller31. The compressed video signal is then delivered to the adder 32. Theinformation amount of the video signal after compression is, forexample, about 1/4 of that of the original video signal. At the sametime, the free amount of information in video signal recording, which isthe difference between the reference amount of video signal informationset by the controller 31 and the estimated amount of information givenfrom the information amount estimation circuit 43, is fed back to thecontroller 31.

On the other hand, the audio signal (about 4 Mbps) digitized by theaudio A/D converter 2 is delivered to the audio interleave 23 whichdivides the audio signal into blocks and which performs shuffling oneach of the blocks, as in the case of the video signal. The audio signalthen undergoes the orthogonal transformation, information amountestimation, variable-length encoding, etc. which are performed by theaudio high-efficiency encoder 24, the same processing as performed forthe video signal. At the same time, as in the case of the video signal,the free amount of information in audio signal recording, which is thedifference between the reference amount of audio signal information setby the controller 31 and the estimated amount of information given fromthe information amount estimation circuit 43, is fed back to thecontroller 31. The high-efficiency encoded video and audio signals arecombined through the adder 32. The combined data is error-correctionencoded by the error-correction encoder 25, encoded by the modulator 7for recording, and recorded on the magnetic tape 8 by means of themagnetic head 10 mounted on the rotating drum 9.

The following describes how the controller 31 controls the amounts ofinformation for recording. First, in the case of a four-channel audiosignal, for example, the reference amounts of information are set, 24Mbps for the video signal of 100 Mbps and 1 Mbps for the audio signal of4 Mbps, and the thus set reference amounts of information arerespectively supplied to the subtractor 46 and the video high-efficiencydecoder 27 for the video signal and to the subtractor 47 and the audiohigh-efficiency decoder 29 for the audio signal. It is well known thatthe information amount of the video signal decreases greatly aftercompression as the image nears a static image. For example, in the abovecompression of the video signal from 100 Mbps to 24 Mbps, the data sizemay be compressed to several Mbps depending on the kinds of image. Forthe audio signal also, the amount of information decreases drasticallyfor muted sections. However, since there are no correlations between thevideo signal and the audio signal, control is performed in the presentembodiment in such a manner that when the information amount of thevideo signal after compression becomes smaller than the reference amountof information (predetermined reduction rate), part of the video signalrecording area on the recording medium (magnetic tape 8) is freed up forrecording of the audio signal with a lower reduction rate (increasedinformation amount), and that when the information amount of the audiosignal after compression becomes smaller than the reference amount ofinformation (predetermined reduction rate), part of the audio signalrecording area on the recording medium (magnetic tape 8) is freed up forrecording of the video signal with a lower reduction rate (increasedinformation amount); thus, the reduction rates in the videohigh-efficiency encoder 22 and the audio high-efficiency encoder 24 arecontrolled so that the sum of the information amount of the video signaland that of the audio signal is maintained constant when recorded. Morespecifically, the subtractor 46 calculates the difference between thereference amount of information for the video signal set by thereference information amount setting circuit 45 and the feedback valuefrom the audio high-efficiency encoder 24 representing the free amountof information in audio recording, and the difference is fed to thevideo high-efficiency encoder 22, while on the other hand, thesubtractor 47 calculates the difference between the reference amount ofinformation for the audio signal set by the reference information amountsetting circuit 45 and the feedback value from the video high-efficiencyencoder 22 representing the free amount of information in videorecording, and the difference is fed to the audio high-efficiencyencoder 24. Thus, in this embodiment, since the reduction rates of thevideo and audio signals are kept as low as possible, degradation in thevideo and audio signal quality is minimized.

A concrete example of such reduction rate control will now be describedwith reference to FIG. 6. FIG. 6(a) shows the standard reduction rates(reference amounts of information) of the video and audio signals,whereby the video signal of 100 Mbps is compressed to 24 Mbps and theaudio signal of 4 Mbps to 1 Mbps. FIG. 6(b) shows a case in which theinformation amount of the video signal after compression is smaller thanthe reference amount of information (for example, a static imagecontaining a less amount of video information); in this case, the videosignal is compressed from 100 Mbps to 15 Mbps, while the audio signalremains uncompressed, i.e. 4 Mbps. Since the information amount of theoriginal video signal is small, the picture quality would besubstantially the same if the video signal is compressed from 100 Mbpsto 24 Mbps. FIG. 6(c) shows a case in which the information amount ofthe audio signal after compression is smaller than the reference amountof information (for example, a muted section containing no audioinformation); in this case, the audio signal is compressed from 4 Mbpsto 0 Mbps, while the video signal is compressed from 100 Mbps to 25Mbps. Thus, the reduction rate of the video signal in the videohigh-efficiency encoder 22 and the reduction rate of the audio signal inthe audio high-efficiency encoder 24 are controlled so that any freespace containing no information will not be left in the recording areacapable of recording a total amount of information (25 Mbps) and so thatthe reduction rates are kept as low as possible in order to preventdegradation in the picture and sound quality.

Next, the operation of the reproduction system will be described. In thereproduction system, the data reproduced from the magnetic tape 8 by themagnetic head 10 is decoded by the demodulator 11 and is fed to theerror-correction decoder 26 for correcting of errors such as bursterrors that occurred on the magnetic tape 8. If there are uncorrectableerrors, error flags are attached to the data for transfer. Theerror-corrected video and audio signals are separated by the A/Vseparation circuit 13. Next, the video high-efficiency decoder 27expands the compressed video signal based on the reference amount ofinformation given from the controller 31. The expanded video signal isdelivered to the video deinterleave 28 where each of the video blocks isdeshuffled to reconstruct the video block in its original form. Anyvideo block containing an uncorrectable error and therefore attachedwith an error flag undergoes pixel interpolation through theinterpolation circuit 16, and the reconstructed analog video signal isobtained from the video D/A converter 17. On the other hand, the audiosignal separated by the A/V separation circuit 13 is delivered to theaudio high-efficiency decoder 29 which expands the compressed audiosignal on the basis of the reference amount of information given fromthe controller 31. The expanded audio signal is then delivered to theaudio deinterleave 30 where each of the audio blocks is deshuffled toreorder the audio signal into its original form, and the recorded analogaudio signal is obtained from the audio D/A converter 19.

As described above, in the first embodiment, since the reduction ratesof the video and audio signals are controlled so that the sum of theinformation amount of the video signal and that of the audio signal,after high-efficiency encoding, is maintained constant, the video signaland the audio signal can be recorded simultaneously while minimizingdegradation in the picture and sound quality.

Embodiment 2

FIG. 7 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a secondembodiment of the invention. In FIG. 7, the same reference numerals asused in FIG. 3 designate the same or corresponding components. In therecording system, a video error-correction encoder 33 for performingerror-correction encoding of the video signal is inserted between thevideo high-efficiency encoder 22 and the adder 32. Also, a plurality ofaudio A/D converters 2 are provided, one for every one of audiochannels, and between the audio A/D converters 2 and the adder 32, thereare provided: an audio selector 34 for selecting from among a pluralityof audio channels (N channels) the audio channels that should actuallybe recorded; and an audio error-correction encoder 35 for performingerror-correction encoding of the audio signal. In the reproductionsystem, a video error-correction decoder 36 for correcting errors in thevideo signal is inserted between the A/V separation circuit 13 and thevideo high-efficiency decoder 27. Also, a plurality of audio D/Aconverters 19 are provided, one for every one of the audio channels, andbetween the audio D/A converters 19 and the A/V separation circuit 13,there are provided: an audio error-correction decoder 37 for correctingerrors in the audio signal; and an audio distributor 38 for directingthe reproduced audio signal to the selected output terminals (audio D/Aconverters 19). The numeral 31 designates a controller which controlsthe video high-efficiency encoder 22, the audio selector 34, the videohigh-efficiency decoder 27, and the audio distributor 38 in accordancewith the number of selected audio signal channels.

FIG. 8 is a schematic diagram showing the internal configuration of thevideo high-efficiency encoder 22 in the recording system illustrated inFIG. 7. The video high-efficiency encoder 22 comprises: an orthogonaltransform circuit 41 for performing an orthogonal transform, such as aDCT, on each block of the video signal; an information amount estimationcircuit 43 for estimating the information amount of the video signal onthe basis of transform coefficients given from the orthogonal transformcircuit 41 and for supplying a control signal to a variable-lengthencoding circuit 42 so as to achieve the reduction rate directed by thecontroller 31; and the variable-length encoding circuit 42 for encodingthe transform coefficients given from the orthogonal transform circuit41 by adaptively quantizing them in accordance with the control signalgiven from the information amount estimation circuit 43.

Next, the operation of the apparatus will be described. In the recordingsystem, the video signal (about 100 Mbps) digitized, as in the prior artexample, by the video A/D converter 1 is delivered to the videointerleave 21 where the video signal is divided into blocks eachrepresenting a plurality of pixels and shuffling is performed on each ofthe blocks. The thus processed video signal is compressed and encoded bythe video high-efficiency encoder 22. In the video high-efficiencyencoder 22, the video signal that has undergone the orthogonaltransformation through the orthogonal transform circuit 41 is compressedby the variable-length encoding circuit 42, which controls the wordlength, i.e. the number of bits, for quantizing the transformcoefficients, in accordance with the control signal given from theinformation amount estimation circuit 43. After error-correctionencoding by the video error-correction encoder 33, the video signal isfed to the adder 32. On the other hand, from among the plurality ofchannels of the audio signals digitized by the audio A/D converters 2,the channels of the audio signals that should be recorded, for example,two channels or four channels, are selected by the audio selector 34.The audio signals thus selected are fed to the audio error-correctionencoder 35 for error-correction encoding, after which the audio signalsare fed to the adder 32 where the audio signals are combined with thevideo signal. The combined data is encoded by the modulator 7 forrecording, and recorded on the magnetic tape 8 by means of the magnetichead 10 mounted on the rotating drum 9.

In this embodiment, the input video signal of 100 Mbps is compressed forrecording on the magnetic tape 8, whereas the audio signals are recordedwithout compression on the magnetic tape 8. FIG. 9 shows the assignmentof information amounts when recording the video signal (100 Mbps) andaudio signals (two channels and four channels shown) at a fixedrecording information amount of 25 Mbps. As shown, when the number ofaudio signal channels to be recorded increases (the audio informationincreases), the reduction rate in the video high-efficiency encoder 22is raised. Conversely, when the number of audio signal channels to berecorded decreases (the audio information decreases), the reduction ratein the video high-efficiency encoder 22 is lowered. In the case of twochannels (case 1), since the audio information amount is 2 Mbps whenformatted for recording, the video high-efficiency encoder 22 compressesthe video signal of 100 Mbps to 23 Mbps. In the case of four channels(case 2), since the audio information amount is 4 Mbps when formattedfor recording, the video signal of 100 Mbps is compressed to 21 Mbps.When the number of audio signal channels are further increased, thereduction rate of the video signal is raised accordingly. Suchadjustment of the reduction rate in the video high-efficiency encoder 22is controlled by the controller 31. Since the reduction rate of thevideo signal is adjusted to match the change in the number of audiosignal channels, as described above, any desired number of audiochannels can be selected. Also, even when the number of audio channelsis increased from two to four, there occurs almost no degradation in thepicture quality since the reduction rate of the video signal onlyslightly changes, from 23/100 to 21/100.

Examples of recording formats for case 1 and case 2 are shown in FIG.10(a) and FIG. 10(b), respectively. The ratio of the audio recordingarea to the entire recording area changes as the number of audiochannels changes. Also, since the video and audio signals are separatelyencoded for recording, as well as for error-correction, postrecording ispossible in which only audio signals are rerecorded at a later time.

Next, the operation of the reproduction system will be described. In thereproduction system, the data reproduced from the magnetic tape 8 by themagnetic head 10 is decoded by the demodulator 11 and is separated intothe video signal and the audio signal by the A/V separation circuit 13.The separated video and audio signals are supplied to the videoerror-correction decoder 36 and the audio error-correction decoder 37respectively, where errors such as burst errors that occurred on themagnetic tape 8 are corrected. If there are uncorrectable errors, errorflags are attached to the data for transfer. Next, the compressed videosignal is expanded by the video high-efficiency decoder 27 and isdelivered to the video deinterleave 28 where each of the video blocks isdeshuffled to reconstruct the video block in its original form. Anyvideo block containing an uncorrectable error and therefore attachedwith an error flag undergoes pixel interpolation through theinterpolation circuit 16, and the reconstructed analog video signal isobtained from the video D/A converter 17. On the other hand, the audiosignal after error correction is supplied to the audio distributor 38from which the audio signal is delivered to the selected audio D/Aconverters 19 for reproduction of the analog audio signal.

As described above, in the second embodiment, since the reduction rateof the video signal is controlled according to the number of selectedaudio channels so that the sum of the information amount of the videosignal and that of the selected audio signal, after high-efficiencyencoding, is maintained constant, the video signal can be recordedsimultaneously with the audio signal having the desired number ofchannels while minimizing degradation in the picture quality.

Embodiment 3

FIG. 11 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a thirdembodiment of the invention. In FIG. 11, the same reference numerals asused in FIGS. 3 and 7 designate the same or corresponding components. Inthe recording system, the audio selector 34, which selects from among aplurality of digitized audio signal channels (N channels) the audiochannels that should actually be recorded, is provided between theplurality of audio A/D converters 2, provided one for every one of theaudio channels, and the audio interleave 23. In the reproduction system,the audio distributor 38, which directs the reproduced audio signal tothe selected output terminals (audio D/A converters 19), is providedbetween the audio deinterleave 30 and the plurality of audio D/Aconverters 19 provided one for every one of the audio channels. Thecontroller designated by the reference numeral 31, in accordance withthe number of selected audio channels, supplies a control signal to thevideo high-efficiency encoder 22, the audio high-efficiency encoder 24,the audio selector 34, the audio distributor 38, the videohigh-efficiency decoder 27, and the audio high-efficiency decoder 29,while the estimated amounts of information are fed back to thecontroller 31 from; the video and audio high frequency encoders 22 and24.

The internal configuration of the video high-efficiency encoder 22 (orthe audio high-efficiency encoder 24) is the same as that of the firstembodiment illustrated in FIG. 4. FIG. 12 is a schematic diagram showingthe internal configuration of the controller 31 of this embodiment. Theconfiguration shown is the same as that of the controller 31 of thefirst embodiment (see FIG. 5), except that the reference informationamount setting circuit 45 sets the reference amounts of information forthe video and audio signals according to the number of selected audiochannels.

Next, the operation of the apparatus will be described. The operationfor the recording of the video signal is the same as that described inthe first embodiment and therefore, the description thereof is omittedherein. From among the plurality of channels of the audio signalsdigitized by the audio A/D converters 2, the channels of the audiosignals that should be recorded, for example, two channels or fourchannels, are selected by the audio selector 34 and supplied to theaudio interleave 23 which divides the audio signals into blocks anddeshuffles each of the audio blocks. The thus processed audio signalsare compressed by the audio high-efficiency encoder 24 and then fed tothe adder 32. As in the first embodiment, the free amounts ofinformation for the video and audio signals are fed back to thecontroller 31 from the video high-efficiency encoder 22 and the audiohigh-efficiency encoder 24, respectively. Thereafter, the video andaudio signals are recorded on the magnetic tape 8 in the same manner asin the first embodiment.

The following describes how the controller 31 controls the amounts ofinformation for recording. First, the number of selected audio channelsis input to the reference information amount setting circuit 45 in thecontroller 31 shown in FIG. 12. The reduction rates in the videohigh-efficiency encoder 22 and the audio high-efficiency encoder 24 arecontrolled according to the number of audio channels. When the number ofaudio channels increases (the audio information amount increases), thereduction rates are raised; when the number of audio channels decreases(the audio information amount decreases), the reduction rates arelowered. For example, in the case of two channels, the reference amountsof information for compressing the video and audio signals are set to24.5 Mbps for the video signal of 100 Mbps and 0.5 Mbps for the audiosignal of 2 Mbps, and in the case of four channels, the referenceamounts are set to 24 Mbps for the video signal of 100 Mbps and 1 Mbpsfor the audio signal of 4 Mbps. Depending on the kinds of the video andaudio signals, the information amounts after compression may greatlydecrease and become smaller than the reference amounts. In such a case,in order to keep the reduction rates of the video and audio signals aslow as possible, the reduction rates in the video high-efficiencyencoder 22 and audio high-efficiency encoder 24 are controlled so thatthe sum of the information amount of the video signal and that of theaudio signal after compression is maintained constant, as in the firstembodiment. The control process is the same as that described in thefirst embodiment (see FIG. 6), and therefore, the description thereof isomitted herein.

Next, the operation of the reproduction system will be described. Theaudio signal expanded by the audio high-efficiency decoder 29 is readinto the audio deinterleave 30 where each of the audio blocks isdeshuffled to reorder the audio signal into its original form. The audiosignal is then fed to the audio distributor 38 from which it is suppliedto the selected audio D/A converters 19 to reproduce the analog audiosignal. Other operations are the same as in the first embodiment, andtherefore, the description thereof is omitted herein.

As described, in the third embodiment, since the reduction rates of thevideo and audio signals are controlled according to the number ofselected audio channels so that the sum of the information amount of thevideo signal and that of the audio signal, after high-efficiencyencoding, is maintained constant, the video signal can be recordedsimultaneously with the audio signal having the desired number ofchannels while minimizing degradation in the picture and sound quality.

In the above first, second, and third embodiments, the magnetic tape 8is used as the recording medium, but it will be appreciated that theinvention is also applicable for other recording media, such as amagnetic disk, optical disk, semiconductor memory, etc., if the samerecording format is employed and the recording amount of information isfixed.

Embodiment 4

FIG. 13 is a block diagram showing the configuration of a digitalvideo/audio recording and reproducing apparatus according to a fourthembodiment of the invention. In FIG. 13, the same reference numerals asused in FIG. 3 designate the same or corresponding components. In therecording system, a data sorting memory 39 for reordering the componentsof the video and audio signals according to their frequencies isprovided between the adder 32 and the error-correction encoder 25. Inthe reproduction system, a data unsorting memory 40 for reordering thevideo and audio signals back into the original form is provided betweenthe error-correction decoder 26 and the A/V separation circuit 13.

Next, the operation of the apparatus will be described. In thisembodiment, the high frequency components of the video and audio signalsare recorded at the ends of the recording tracks on the magnetic tape 8.The following description focuses on this feature of the embodiment. Thehigh-efficiency encoded video and audio signals are combined in theadder 32 and supplied to the data sorting memory 39 which reorders thecomponents of the encoded video signal in decreasing order of thefrequency and the components of the encoded audio signal in increasingorder of the frequency. The thus reordered signals are error-correctionencoded by the error-correction encoder 25, processed through themodulator 7, and recorded on the magnetic tape 8 by means of themagnetic head 10.

FIG. 14 shows a recording track pattern on the magnetic tape 8 accordingto this embodiment. The arrow in the figure shows the helical scandirection of the rotating magnetic head 10. The magnetic head 10helically scans the surface of the magnetic tape 8 in the arrowdirection (from the bottom to the top of the magnetic tape 8) to recordthe video signal and the audio signal in this order. As a result, thehigh frequency components of the video signal are recorded at theleading end of the recording track, while at the trailing end thereofare recorded the high frequency components of the audio signal.

After error-correction by the error-correction decoder 26, the video andaudio signals are fed to the data unsorting memory 40 which reorders thesignals back into the original form for the subsequent expansion by thehigh-efficiency decoders 27 and 29. The video and audio signals areseparated by the A/V separation circuit 13. Thereafter, the analog videoand audio signals are reproduced for output, in the same manner as inthe first embodiment. The high frequency components of the video signalmainly represent details or the contours of the image. Therefore, if thehigh frequency components of the video signal recorded at the leadingends of the recording tracks contain errors that cannot be completelycorrected by the error-correction decoder 26, such errors are onlymanifested in smeared image contours, etc. and no appreciable errorsappear in the image as a whole. On the other hand, the high frequencycomponents of the audio signal represent the high frequency range of asound. Therefore, if errors remain in the high frequency components ofthe audio signal recorded at the trailing ends of the recording tracks,only a slight drop in the high frequency range is caused in thereproduced sound and no appreciable errors appear in the sound as awhole.

In the above fourth embodiment, both the video and audio signals arehigh-efficiency encoded in a manner similar to that of the firstembodiment, but it will be appreciated that for applications wherehigh-efficiency encoding is performed on either one of the video oraudio signal, the same effects as described above can be obtained forthe video signal (or the audio signal) if the high frequency componentsof the video signal (or the audio signal) after high-efficiency encodingare recorded at one end of each recording track.

As described, in the fourth embodiment, since the high frequencycomponents of the high-frequency encoded video and audio signals arerecorded at the ends of the recording tracks on the magnetic tape, thevideo and audio signal can be recorded simultaneously while preventingappreciable errors from appearing in the reproduced image or sound andthus minimizing degradation in the picture and sound quality.

In the above embodiments, the orthogonal transform such as a DCT is usedin performing high-efficiency encoding on the video and audio signals.However, a sub-band division method making use of a sub-band filter maybe used, if the method is used, the same advantages can be obtained.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiments are therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and boundsthereof are therefore intended to be embraced by the claims.

What is claimed is:
 1. A digital video/audio reproducing apparatus forreproducing encoded signals obtained by encoding a digitized videosignal and a digitized audio signal at a fixed amount of information perunit time to reproduce an original video signal and an original audiosignal which were encoded by a video encoder and an audio encoder suchthat a sum of a varying information amount of the encoded digitizedvideo signal and a varying information amount of the encoded digitizedaudio signal was maintained constant and such that the varyinginformation amount of the encoded digitized video signal output from thevideo encoder was dependent on an output of the audio encoder.
 2. Thedigital video/audio reproducing apparatus of claim 1, wherein theencoded digitized video signal and the encoded digitized audio signalare stored on one of the magnetic tape, magnetic disk, optical disk, andsemiconductor memory.
 3. A digital video/audio reproducing apparatus forreproducing encoded signals obtained by encoding a digitized video and adigitized audio signal at a fixed amount of information per unit time,said digital video/audio reproducing apparatus comprising:first decodingmeans for expanding and decoding the encoded digitized video signal witha first variable expansion rate; second decoding means for expanding anddecoding the encoded digitized audio signal with a second variableexpansion rate; and control means for controlling the first and secondexpansion rates in said first and said second decoding means toreproduce an original video signal and an original audio signal whichwere encoded by a video encoder and an audio encoder so that a sum of avarying information amount of the encoded digitized video signal and avarying information amount of the encoded digitized audio signal wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 4. The digital video/audioreproducing apparatus of claim 3, wherein the encoded digitized videosignal and the encoded digitized audio signal are stored on one of amagnetic tape, magnetic disk, optical disk, and semiconductor memory. 5.The digital video/audio reproducing apparatus of claim 3, wherein theencoded digitized video signal and the encoded digitized audio signalwere recorded so that when the information amount of the encodeddigitized video signal is smaller than a reserved video informationamount, the encoded digitized audio signal is recorded in a recordingarea originally provided for recording the encoded digitized videosignal, and so that when the information amount of the encoded digitizedaudio signal is smaller than a reserved audio information amount, theencoded digitized video signal is recorded in a recording areaoriginally provided for recording the encoded digitized audio signal. 6.A digital video/audio reproducing apparatus for reproducing encodedsignals obtained by encoding a digitized video signal and a digitizedmulti-channel audio signal at a fixed amount of information per unittime, said digital video/audio reproducing apparatus comprising:decodingmeans for decoding the encoded digitized video signal with a variableexpansion rate; means for identifying a number of digitized audiosignals to be reproduced from the digitized multi-channel audio signal;and means for controlling the expansion rate in said decoding meansaccording to the number of digitized audio signals to reproduce anoriginal video signal and an original multi-channel audio signal whichwere encoded by a video encoder and an audio encoder so that a sum of avarying information amount of the encoded digitized video signal and avarying information amount of the number of digitized audio signals wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 7. The digital video/audioreproducing apparatus of claim 6, wherein the encoded digitized videosignal and the number of digitized audio signals are stored on one of amagnetic tape, magnetic disk, optical disk, and semiconductor memory. 8.A digital video/audio reproducing apparatus for reproducing encodedsignals obtained by encoding a digitized video signal and a digitizedmulti-channel audio signal at a fixed amount of information per unittime, said digital video/audio reproducing apparatus comprising:firstdecoding means for expanding and decoding the encoded digitized videosignal with a first variable expansion rate; means for identifying anumber of digitized audio signals to be reproduced from the encodeddigitized multi-channel audio signal; second decoding means forexpanding and decoding the number of digitized audio signals with asecond variable expansion rate; and control means for controlling thefirst and second expansion rates in said first and said second decodingmeans to reproduce an original video signal and an originalmulti-channel audio signal which were encoded by a video encoder and anaudio encoder so that a sum of a varying information amount of theencoded digitized video signal and a varying information amount of thenumber of digitized audio signals was maintained constant and such thatthe varying information amount of the encoded digitized video signaloutput from the video encoder was dependent on an output of the audioencoder.
 9. The digital video/audio reproducing apparatus of claim 8,wherein the encoded digitized video signal and the number of digitizedaudio signals are stored on one of a magnetic tape, magnetic disk,optical disk, and semiconductor memory.
 10. The digital video/audioreproducing apparatus of claim 8, wherein the encoded digitized videosignal and the number of digitized audio signals were recorded so thatreduction rates of the encoded digitized video signal and encodeddigitized multi-channel audio signal increase when a number of audiosignal channels selected for encoding increases, and decrease when thenumber of audio signal channels selected for encoding decreases, so thatwhen the information amount of the encoded digitized video signal issmaller than a reserved video information amount, the number of theaudio signals selected for encoding can be recorded in a recording areaoriginally provided for recording the encoded digitized video signal andso that when the information amount of the number of audio signalsselected for encoding is smaller than a reserved audio data amount, theencoded digitized video signals can be recorded in a recording areaoriginally provided for recording the number of audio signals selectedfor recording.
 11. A digital video/audio reproducing apparatuscomprising:first decoding means for expanding and decoding an encodeddigitized video signal with a first expansion rate; second decodingmeans for expanding and decoding an encoded digitized audio signal witha second expansion rate; and control means for controlling the first andsecond expansion rates in said first and said second decoding means toreproduce an original video signal and an original audio signal whichwere encoded by a video encoder and an audio encoder so that a sum of avarying information amount of the encoded digitized video signal and avarying information amount of the encoded digitized audio signal wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 12. The digital video/audioreproducing apparatus of claim 11, wherein the encoded digitized videosignal and the encoded audio signal are reproduced from one of amagnetic tape, magnetic disk, optical disk, and semiconductor memory.13. The digital video/audio reproducing apparatus of claim 11, whereinthe encoded digitized video signal and the encoded audio signal wererecorded so that when the information amount of the encoded digitizedvideo signal is smaller than a reserved video data amount, the encodeddigitized audio signal is recorded in a recording area originallyprovided for recording the encoded digitized video signal, and so thatwhen the information amount of the encoded digitized audio signal issmaller than a reserved audio data amount, the encoded digitized videosignal is recorded in a recording area originally provided for recordingthe encoded digitized audio signal.
 14. The digital video/audioreproducing apparatus of claim 11, wherein said second decoding meansreproduces an original audio signal which was encoded such that thevarying information amount of the encoded digitized audio signal outputfrom the audio encoder is dependent on an output of the video encoder.15. The digital video/audio reproducing apparatus of claim 11, whereinthe varying information amount of the encoded digitized audio signalvaries according to a character of the audio data.
 16. The digitalvideo/audio reproducing apparatus of claim 11, wherein the output of theaudio encoder is a free amount of audio information.
 17. The digitalvideo/audio reproducing apparatus of claim 11, wherein the output of theaudio encoder is a function of an estimated amount of audio information.18. The digital video/audio reproducing apparatus of claim 11, whereinsaid control means limits a total combined data amount of the varyinginformation amount of the encoded digitized audio signal and the varyinginformation amount of the encoded digitized video signal to no more thana predetermined amount by controlling the video encoder to variablycompress the varying information amount of the encoded digitized videosignal, where the predetermined amount is less than a sum of a maximumaudio capacity and a maximum video capacity.
 19. The digital video/audioreproducing apparatus of claim 18, wherein the maximum audio capacity isless than the predetermined amount.
 20. The digital video/audioreproducing apparatus of claim 18, wherein said control means limits thetotal combined data amount of the varying information amount of theencoded digitized audio signal and the varying information amount of theencoded digitized video signal to no more than the predetermined amountby also controlling the audio encoder to variably compress the varyinginformation amount of the encoded digitized audio signal.
 21. Thedigital video/audio reproducing apparatus of claim 11, wherein thevarying information amount of the encoded digitized video signal variesaccording to a character of the video data.
 22. A digital video/audioreproducing apparatus comprising:decoding means for expanding anddecoding an encoded digitized video signal with an expansion rate; meansfor identifying a number of digitized audio signals to be reproducedfrom a multi-channel audio signal; and means for controlling theexpansion rate in said decoding means according to the number ofdigitized audio signals, to reproduce an original video signal and anoriginal multi-channel audio signal which were encoded by a videoencoder and an audio encoder so that a sum of a varying informationamount of the encoded digitized video signal and a varying informationamount of the number of digitized audio signals was maintained constantand such that the varying information amount of the encoded digitizedvideo signal output from the video encoder was dependent on an output ofthe audio encoder.
 23. The digital video/audio reproducing apparatus ofclaim 22, wherein the encoded digitized video signal and the number ofdigitized audio signals are stored on one of a magnetic tape, magneticdisk, optical disk, and semiconductor memory.
 24. The digitalvideo/audio reproducing apparatus of claim 22, wherein the varyinginformation amount of the encoded digitized audio signal variesaccording to a number of supplied audio channels.
 25. A digitalvideo/audio reproducing apparatus comprising:first decoding means forexpanding and decoding an encoded digitized video signal with a firstexpansion rate; means for identifying a number of digitized audiosignals to be reproduced from a multi-channel audio signal; seconddecoding means for expanding and decoding the number of audio signalswith a second expansion rate; and control means for controlling thefirst and second expansion rates in said first and said second decodingmeans to reproduce an original video signal and an originalmulti-channel audio signal which were encoded by a video encoder and anaudio encoder so that a sum of a varying information amount of theencoded digitized video signal and a varying information amount of thenumber of digitized audio signals was maintained constant and such thatthe varying information amount of the encoded digitized video signaloutput from the video encoder was dependent on an output of the audioencoder.
 26. The digital video/audio reproducing apparatus of claim 25,wherein the encoded digitized video signal and the number of audiodigitized signals are stored on one of a magnetic tape, magnetic disk,optical disk, and semiconductor memory.
 27. The digital video/audioreproducing apparatus of claim 25, wherein the encoded digitized videosignal and the number of digitized audio signals were recorded so thatreduction rates of the encoded digitized video signal and encodeddigitized multi-channel audio signal increase when a number of digitizedaudio signal channels selected for recording increases, and decreasewhen the number of digitized audio signal channels selected forrecording decreases, so that when the information amount of the encodeddigitized video signal is smaller than a reserved video data amount, thenumber of the digitized audio signals selected for recording can berecorded in a recording area originally provided for recording theencoded digitized video signal and so that when the information amountof the number of digitized audio signals selected for recording issmaller than a reserved audio data amount, the encoded digitized videosignal can be recorded in a recording area originally provided forrecording the number of digitized audio signals selected for recording.28. A method of reproducing encoded signals obtained by encoding adigitized video and a digitized audio signal at a fixed amount ofinformation per unit time, said method comprising the steps of:(a)expanding and decoding the encoded digitized video signal with a firstvariable expansion rate; (b) expanding and decoding the encodeddigitized audio signal with a second variable expansion rate; and (c)controlling the first and second expansion rates in said steps (a) and(b) to reproduce an original video signal and an original audio signalwhich were encoded by a video encoder and an audio encoder so that a sumof a varying information amount of the encoded digitized video signal avarying information amount of the encoded digitized audio signal wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 29. The method of claim 28,wherein the encoded digitized video signal and the encoded digitizedaudio signal are stored on one of a magnetic tape, magnetic disk,optical disk, and semiconductor memory.
 30. The method of claim 28,wherein the encoded digitized video signal and the encoded digitizedaudio signal were recorded so that when the information amount of theencoded digitized video signal is smaller than a reserved videoinformation amount, the encoded digitized audio signal is recorded in arecording area originally provided for recording the encoded digitizedvideo signal, and so that when the information amount of the encoderdigitized audio signal is smaller than a reserved audio informationamount, the encoded digitized video signal is recorded in a recordingarea originally provided for recording the encoded digitized audiosignal.
 31. A method of reproducing encoded signals obtained by encodinga digitized video signal and a digitized multi-channel audio signal at afixed amount of information per unit time, said method comprising thesteps of:(a) decoding the encoded digitized video signal with a variableexpansion rate; (b) identifying a number of digitized audio signals tobe reproduced from the digitized multi-channel audio signal; and (c)controlling the expansion rate in said steps (a) and (b) according tothe number of digitized audio signals to reproduce an original videosignal and an original multi-channel audio signal which were encoded bya video encoder and an audio encoder so that a sum of a varyinginformation amount of the encoded digitized video signal and a varyinginformation amount of the number of digitized audio signals wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 32. The method according toclaim 31, wherein the encoded digitized video signal and the number ofdigitized audio signals are stored on one of a magnetic tape, magneticdisk, optical disk, and semiconductor memory.
 33. A method ofreproducing encoded signals obtained by encoding a digitized videosignal and a digitized multi-channel audio signal at a fixed amount ofinformation per unit time, said method comprising the steps of:(a)expanding and decoding the encoded digitized video signal with a firstvariable expansion rate; (b) identifying a number of digitized audiosignals to be reproduced from the encoded digitized multi-channel audiosignal; (c) expanding and decoding the number of digitized audio signalswith a second variable expansion rate; and (d) controlling the first andsecond expansion rates in said steps (a) and (c) to reproduce anoriginal video signal and an original multi-channel audio signal whichwere encoded by a video encoder and an audio encoder so that a sum of avarying information amount of the encoded digitized video signal and avarying information amount of the number of digitized audio signals wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 34. The method of claim 33,wherein the encoded digitized video signal and the number of digitizedaudio signals are stored on one of a magnetic tape, magnetic disk,optical disk, and semiconductor memory.
 35. The method of claim 33,wherein the encoded digitized video signal and the number of digitizedaudio signals were recorded so that reduction rates of the encodeddigitized video signal and encoded digitized multi-channel audio signalincrease when a number of audio signal channels selected for encodingincreases, and decrease when the number of audio signal channelsselected for encoding decreases, so that when the information amount ofthe encoded digitized video signal is smaller than a reserved videoinformation amount, the number of the audio signals selected forencoding can be recorded in a recording area originally provided forrecording the encoded digitized video signal and so that when theinformation amount of the number of audio signals selected for encodingis smaller than a reserved audio data amount, the encoded digitizedvideo signals can be recorded in a recording area originally providedfor recording the number of audio signals selected for recording.
 36. Amethod comprising the steps of:(a) expanding and decoding an encodeddigitized video signal with a first expansion rate; (b) expanding anddecoding an encoded digitized audio signal with a second expansion rate;and (c) controlling the first and second expansion rates in said steps(a) and (b) to reproduce an original video signal and an original audiosignal which were encoded by a video encoder and an audio encoder sothat a sum of a varying information amount of the encoded digitizedvideo signal a varying information amount of the encoded digitized audiosignal was maintained constant and such that the varying informationamount of the encoded digitized video signal output from the videoencoder was dependent on an output of the audio encoder.
 37. The methodof claim 36, wherein the encoded digitized video signal and the encodedaudio signal are reproduced from one of a magnetic tape, magnetic disk,optical disk, and semiconductor memory.
 38. The method of claim 36,wherein the encoded digitized video signal and the encoded digitizedaudio signal were recorded so that when the information amount of theencoded digitized video signal is smaller than a reserved video dataamount, the encoded digitized audio signal is recorded in a recordingarea originally provided for recording the encoded digitized videosignal, and so that when the information amount of the encoded digitizedaudio signal is smaller than a reserved audio data amount, the encodeddigitized video signal is recorded in a recording area originallyprovided for recording the encoded digitized audio signal.
 39. A methodcomprising the steps of:(a) expanding and decoding an encoded digitizedvideo signal with an expansion rate; (b) identifying a number ofdigitized audio signals to be reproduced from a multi-channel audiosignal; and (c) controlling the expansion rate in said step (a)according to the number of digitized audio signals, to reproduce anoriginal video signal and an original multi-channel audio signal whichwere encoded by a video encoder and an audio encoder so that a sum of avarying information amount of the encoded digitized video signal and avarying information amount of the number of digitized audio signals wasmaintained constant and such that the varying information amount of theencoded digitized video signal output from the video encoder wasdependent on an output of the audio encoder.
 40. The method of claim 39,wherein the encoded digitized video signal and the number of digitizedaudio signals are stored on one of a magnetic tape, magnetic disk,optical disk, and semiconductor memory.
 41. A method comprising thesteps of:(a) expanding and decoding an encoded digitized video signalwith a first expansion rate; (b) identifying a number of digitized audiosignals to be reproduced from a multi-channel audio signal; (c)expanding and decoding the number of audio signals with a secondexpansion rate; and (d) controlling the first and second expansion ratesin said steps (a) and (c) to reproduce an original video signal and anoriginal multi-channel audio signal which were encoded by a videoencoder and an audio encoder so that a sum of a varying informationamount of the encoded digitized video signal a varying informationamount of the number of digitized audio signals was maintained constantand such that the varying information amount of the encoded digitizedvideo signal output from the video encoder was dependent on an output ofthe audio encoder.
 42. The method of claim 41, wherein the encodeddigitized video signal and the encoded audio signal are reproduced fromone of a magnetic tape, magnetic disk, optical disk, and semiconductormemory.
 43. The method of claim 41, wherein the encoded digitized videosignal and the encoded digitized audio signal were recorded so that whenthe information amount of the encoded digitized video signal is smallerthan a reserved video data amount, the encoded digitized audio signal isrecorded in a recording area originally provided for recording theencoded digitized video signal, and so that when the information amountof the encoded digitized audio signal is smaller than a reserved audiodata amount, the encoded digitized video signal is recorded in arecording area originally provided for recording the encoded digitizedaudio signal.